Jim Miller pointed out on 8 August that “It is well established
that the acoustic information used by a listener to identify a
consonant or a vowel is overlapping and distributed acoustically
across a considerable span of time.” He indicated that although some
have attempted to identify the acoustic locations of consonants and
vowels in running speech, they have for the most part failed since
coarticulation extends well into adjacent phonemes. But if the
question is changed from “acoustic” boundaries to “perceptual”
boundaries, the task becomes rather easy.

When a sentence is abruptly terminated, the last speech sound
is easily perceived. By using an arbitrary starting point before the
beginning of a recorded sentence, and moving the time of the cutoff
through the sentence, it is easy to map the perceptual beginning and
end of each phoneme within a few milliseconds. We have been using
this procedure for several decades.